Polyester-block copolymer is a thermoplastic elastomer, and since the shaped-articles made of polyester-block copolymer show an appropriate superficial hardness and are excellent in impact strength and tenacity, the copolymer is used for various purposes.
However, due to the low melt-viscosity of polyester-block copolymer in general, in the fields where a high melt-viscosity of the material is demanded, for instance, in the case of shape-forming the material by blow-molding or "profile-extruding", it is frequently difficult to obtain the qualified shaped articles from polyester-block copolymer because of the drawdown of the melt resin. Accordingly, methods for improving the processability of polyester-block copolymer in shape-forming while retaining the inherent favorable properties of the resin, have been hitherto studied. For instance, trials have been carried out for solving the problem by admixing an ABS resin (terpolymer of acrylonitrile, butadiene and styrene) or an MBS resin (terpolymer of methyl methacrylate, butadiene and styrene) with polyester-block copolymer.
Although one of the properties, namely, the processability of polyester-block copolymer is improved by the admixture of ABS- or MBS-resin, on the other hand, an unfavorable phenomenon of the occurrence of roughness on the surface of the shaped articles made of the composition comprising polyester-block copolymer and ABS- or MBS-resin has been recognized. The phenomenon includes undesirable defects of the occurrence of so-called fish-eyes due to the poorly dispersed material in the surface layer of the shaped articles resulting in spoiling the appearance of the shape-formed articles. The occurrence of roughness of the surface of the shape-formed articles is considered to be attributable to the insufficient mixing and kneading of the composition comprising polyester-block copolymer and ABS- or MBS-resin.
In order to improve the insufficient mixing and kneading, reinforcement of the conditions of mixing and kneading and addition of a lubricant are considered, however, the former is apt to lead to deterioration of the material and the latter is in danger of causing bleeding of the lubricant onto the surface of the shape-formed articles.
As a result of enthusiastic studies of the present inventors for the improvement of the foregoing defects in polyester-block copolymers, it has been found that a composition comprising 95 to 20% by weight of polyester-block copolymer and 5 to 80% by weight of at least one graft-copolymer prepared by graft-copolymerizing a monomeric mixture predominantly consisting essentially of styrene and methyl methacrylate and containing 0.01 to 3.0% by weight of a cross-linking agent with a cross-linked elastomeric trunk polymer containing not less than 50% by weight of rubber like segment selected from the group consisting of butadiene unit and C.sub.4 to C.sub.10 -alkyl acrylate units and 0.01 to 3.0% by weight of a cross-linking agent is a resin composition showing an improved processability in shape-forming while retaining the desirable properties of the original polyester-block copolymer and giving a smaller degree of surface-roughness under condition of mixing and kneading of a relatively low degree and an improved weather proofness to the shape-formed articles especially when alkyl-acrylate graft polymer is admixed. The present invention has been completed while being based on the findings.
Accordingly, the main object of the present invention is to provide a composition of polyester-block copolymer excellent in processability for manufacturing shape-formed articles. Another object of the present invention is to provide a composition of polyester-block copolymer which gives shape-formed articles showing smooth surfaces without fish-eyes and the like even under conditions of mixing and kneading of a low degree.